Its a tiny share of the entire gaming market when you stop pretending consoles and PC are the only games.
Highguard was trying to make it in the market you describe, with PvP players who already have games they know and love, and Highguard offers nothing new, nothing interesting, and therefor zero reason to swap to a new game.
PvP games are popular on the console/PC market, but they are tiny once you look at the actual global gaming market, in particular if you include mobile gaming. Nobody can tell me Highguard ever had a realistic chance to make it on the PC/Console market where it has to compete with entrenched games that have been running professional leagues and tournaments for years at this point, or were launched with a popular IP tied to it.
Highguard was not good enough to make it in the market they aimed at, and they must have known that. They should have developed the game for mobile phones instead, make it about PvE lootbox raiding, even an auto battler would have done better than the released game. There are way more players in that market than on Steam.
Raid: Shadow Legends (mobile) is still alive and has more players daily than any of the PvP games on steam.